Certain deep hole drilling systems such as gun drills, single tube drilling systems, and double tube drilling systems are known in the art. These deep hole drilling systems may be used for drilling holes with a large depth to diameter ratio.
A single tube system, or STS drilling system may be used to drill holes having large depth to diameter ratios with improved penetration rates, hole size accuracy, and straightness over gun drills. At the same time, such systems have various disadvantages, such as tending to cut on themselves, due to a single effective cutting edge. This causes significant stresses. Additionally, such systems may utilize a wear pad, which due to the configuration, tends to bear on the sides of the formed hole during cutting with significant force, such that the wear pad tends to cause hardening of the hole and embrittlement of the material. This may be termed work hardening of the hole, which is undesirable. The STS drilling system may include a drilling head, a boring shank, or tube, and a pressure head. The drilling head may be threaded onto the tube, the inside of the tube being in communication with one or more apertures through the drilling head. In operation, the pressure head may force cutting fluid between the outside of the tube and the hole wall. The cutting fluid may be evacuated along with chips created by the drilling process through the drilling head and up through the center of the tube.
The STS requires a cutting fluid delivery system for providing a volume of cutting fluid at pressures of up to 1000 pounds per square inch (about 689.4 kilopascals) or more. The pressure head introduces cutting fluid between the tube and the hole wall. To maintain pressure in the cavity, the pressure head may seal against the part being drilled to produce a water tight seal. In one sealing embodiment, the part being drilled may have a flat area around the drilled hole for the pressure head to seal.
A Double Tube System, or DTS drilling system, also known as an Ejector System, is based on similar principles as the Single Tube System. Both systems may utilize a cylindrical body design and evacuate cutting fluid and chips internally. The DTS system may use less cutting fluid pressure and volume.
The DTS drilling system may include a drilling head, an outer tube, an inner tube, and a rotating or non-rotating machine connection. The drilling head may be threaded onto the outer tube, with the inner tube in communication with one or more apertures through the drilling head. Both the inner and outer tubes are retained by the machine tool connector. Cutting fluid is channeled through the machine tool connector and between the outer tube and the inner tube. A portion of the cutting fluid is directed internally into the inner tube through venturi slots manufactured into the inner tube wall. The remaining cutting fluid proceeds to the cutting edge in order to cool and lubricate the tool. The cutting fluid diverted through the venturi slots creates a low pressure area in the inner tube drawing cutting fluid and chips from the cutting edge through the drilling head and into the inner tube. This vacuum-like phenomena may reduce the amount of cutting fluid pressure and volume by up to 50% or more. Certain DTS system embodiments may be used for holes that are about 0.75 inches (about 19 millimeters) in diameter or larger.
The drilling heads for STS and DTS drilling systems may comprise a threaded tool body with chip evacuation inlet apertures, one or more cutting edges, and one or more wear pads. The cutting edges in the prior art have included hardened steel cutting edges or a plurality of inserts. Drilling heads in the prior art contain cutting edges that are difficult to replace or re-sharpen, and are discarded after the cutting edges are worn.
There remains a need for STS and DTS drilling systems to overcome these and other disadvantages of the prior art.
A drilling head according to an example of the present invention is disclosed for a tubular shank having an inside diameter and threads comprising an axial body having a duct exiting through a first end. Threads adjacent the first end corresponding to the threads on the shank align the duct with the shank inside diameter. A bore is provided from an outer surface of the body to the duct; and two axially extending approximately parallel and offset surfaces adjacent a second end. An insert is affixed between the offset surfaces, the insert comprising: a first face at least partially contacting one offset surface and a second face at least partially contacting the other offset surface; one or more cutting edges adjacent the first face, the second face, or both; and a cutting lip adjacent one or more cutting edges.